Posttraumatic stress disorder (PTSD) is common and debilitating. Because the development of PTSD is conditional on trauma exposure, PTSD may be the most preventable of mental disorders. We have the unique opportunity to reduce the population burden of PTSD by both by preventing trauma exposure and by delivering timely interventions to those most at risk in the aftermath of exposure. However, limitations of extant epidemiologic studies have hindered progress in our understanding of when, where and how to intervene - with regard to PTSD. This application seeks support for a program of research that examines the prevalence of and risk and protective factors for the three stages of PTSD: trauma exposure, onset, and chronic course. This project uses data from the coordinated national population surveys participating in the World Mental Health (WMH) Survey Initiative. The unprecedented size, representativeness, and richness of the WMH database provide a unique opportunity to develop a comprehensive model of PTSD etiology. We will validate this model using longitudinal data from the National Comorbidity Survey panel sample (NCSII). Analyses will address the following specific aims: 1) Determine the cross- national public health burden of PTSD in relation to specific types of traumatic event; 2) Develop a model of the etiology of trauma exposure and PTSD; 3) Identify factors associated with PTSD chronicity, severity, and the development of subsequent comorbid disorders. Through accomplishment these aims, we will identify malleable and robust risk factors for the different phases of PTSD and provide novel information on how cultural diversity influences each of these phases. The results are expected to generate significant progress in scientific, clinical, and policy efforts aimed at the prediction and prevention of PTSD.